As is known, microcellular injection molding is a process wherein a supercritical fluid is introduced into a liquid polymer prior to the polymer being injected into a mold. The polymer solidifies in the mold to form a desired component. The introduction of the supercritical fluid prior to injection of the polymer into the mold causes tiny bubbles to be distributed throughout the molded component. By providing tiny bubbles in the molded component, the amount of material necessary to mold the component is reduced, while the dimensional stability of the molded component is improved. Hence, this microcellular injection molding process, often referred to as “microcellular foaming,” allows for the production of lightweight and dimensionally stable plastic components with complex geometries while reducing the amount of raw material.
By way of example, Xu, U.S. Pat. No. 6,322,347 discloses a system and a method for the production of foams, and, in particular microcellular foams. The systems include a restriction element that reduces the backflow of polymer melt in an extruder while polymeric material is injected into a mold or ejected from a die. The restriction element is positioned upstream of a blowing agent injection port to maintain the solution of polymer and blowing agent in the extruder above a minimum pressure throughout an injection or ejection cycle, and preferably above the critical pressure required for the maintenance of a single-phase solution of polymer and blowing agent. Typically, the blowing agent is a gas, e.g., nitrogen gas, in its supercritical state. It is contemplated for the system to be used in injection molding, blow molding, or any other processing technique that includes injection or ejection cycles. In some embodiments, the system utilizes a reciprocating screw for injection or ejection of the single-phase solution. In other embodiments, the system includes an accumulator connected to an outlet of the extruder, in which a plunger moves to inject polymeric material into a mold or eject polymeric material from a die.
While functional for its intended purpose, the system and method disclosed in the '347 patent has certain disadvantages. Initially, it is noted that specialized equipment disclosed in the '347 patent, along with the need for supercritical fluids or blowing agents, increases the price of this technology. Further, the surface quality of components fabricated in accordance with the system and method of the '347 patent have a tendency to be irregular and/or rough. As such, there exists a need for a method of fabricating injection molded components which costs less and which produces components with better surface quality than current methods.
Therefore, it is a primary object and feature of the present invention to provide a method for fabricating injection molded components.
It is a further object and feature of the present invention to provide a method for fabricating injection molded components which produces components having better surface qualities than those components produced by current methods.
It is a still further object and feature of the present invention to provide a method for fabricating injection molded components which produces lightweight components with comparable properties as those produced by current methods, but at a lower cost.
It is a still further object and feature of the present invention to provide a method for fabricating injection molded components which is simple and may be performed with standard injection molding machinery.
In accordance with the present invention, a method of fabricating an injection-molded component is provided. The method includes the step of introducing a liquid, a nucleating agent and a polymer into an injection barrel of an injection molding machine. The liquid, the nucleating agent and the polymer are injected into a mold corresponding in shape to the component and the component is released from the mold.
The injection molding machine includes a hopper communicating with the injection barrel. The liquid, the nucleating agent and the polymer are introduced into the hopper prior to introduction in the injection barrel. Thereafter, the polymer is plasticized in the injection barrel. It is contemplated for the liquid to be water and for the nucleating agent to be a salt, although common fillers such as talc and nanoclay may also used. The nucleating agent may be dispersed in the liquid prior to introduction into the injection barrel and/or dissolved in the liquid prior to introduction into the injection barrel. An additive may also be introduced into the injection barrel. The additive alters a physical characteristic of the formed component.
In accordance with a further aspect of the present invention, a method of fabricating an injection-molded component is provided. The method includes the steps of dispersing a nucleating agent in a liquid, and introducing the liquid and a polymer into an injection barrel of an injection molding machine. The liquid and the polymer are injected into a mold corresponding in shape to the component. Thereafter, the component is released from the mold.
The injection molding machine includes a hopper communicating with the injection barrel. The liquid with the nucleating agent dispersed therein and the polymer are introduced into the hopper prior to introduction in the injection barrel. Thereafter, the polymer is plasticized in the injection barrel. It is contemplated for the liquid to be water and for the nucleating agent to be a salt, such as sodium chloride, although common fillers such as talc and nanoclay may also be used as the nucleating agent. The nucleating agent may be dispersed in the liquid by dissolution in the liquid. An additive may also be introduced into the injection barrel. The additive alters a physical characteristic of the formed component.
In accordance with a still further aspect of the present invention, a method of fabricating an injection-molded component is provided. The method includes the step of introducing the liquid and a polymer into an injection barrel of an injection molding machine. The polymer is plasticized in the injection barrel, and the liquid and the polymer are injected into a mold corresponding in shape to the component. Thereafter, the component is released from the mold.
The injection molding machine includes a hopper communicating with the injection barrel. The liquid, the nucleating agent and the polymer are introduced into the hopper prior to introduction in the injection barrel. It is contemplated for the liquid to be water and for the nucleating agent to be a salt, although common fillers such as talc and nanoclay may also be used as the nucleating agent. The nucleating agent may be dispersed in the liquid prior to introduction into the injection barrel and/or dissolved in the liquid prior to introduction into the injection barrel. An additive may also be introduced into the injection barrel. The additive alters a physical characteristic of the formed component.